1. Field of the Invention
The present invention relates to an apparatus and a method for ultrasonic detection of internal flaws of a manufactured steel plate.
2. Discussion of Related Art
In a thick plate factory, ultrasonic detection is used in a quality control process before product shipment in order to detect internal flaws in manufactured steel plates. The ultrasonic detection is a method for determining whether flaws including cracks, intervening materials, segregations, etc. are present in steel plates by transmitting ultrasonic waves to the steel plates and receiving as well as analyzing ultrasonic waves reflected by the steel plates.
The ultrasonic detection may be divided into contact type detection methods and noncontact type detection methods depending on whether or not an ultrasonic probe contacts a steel plate surface.
In the case of the contact type detection methods, misdetections frequently occur because of noise occurrences due to surface conditions and shapes of a steel plate, and a deterioration of the detection performance and a reduction of the life of an ultrasonic probe occur due to abrasions of the detection surface of the probe due to frictions between the ultrasonic probe and the steel plate.
To overcome such limitations of the contact type detection methods, various noncontact type detection methods are being considered. In the case of the noncontact detection methods, a contact medium is necessary to transfer ultrasonic energy oscillated by an ultrasonic probe, and as a representative medium, there is water with excellent ultrasonic wave transmission efficiency.
FIG. 1 illustrates a submersible ultrasonic detection method among noncontact ultrasonic detection methods for detecting flaws in steel plates.
As shown in FIG. 1, a steel plate 3 is submerged in a bath 1 filled with water, and ultrasonic detection is performed above the steel plate 3 using a submersion type ultrasonic probe 2. Accordingly, since the entire steel plate 3 is under water, even when the ultrasonic probe 2 moves, there is an advantage where it is possible to maintain constant efficiency of transmitting and receiving ultrasonic waves.
However, in the case of applying the submersing ultrasonic detection method to a process of producing thick plates in a steel mill, a bath 1 with a large size for submersing the steel plate 3 transported by a roll 4 and a vertical movement device 5 for vertically moving the steel plate 3 in the bath 1 are necessary. For this, a large-scale construction work for structurally changing the facilities of the steel mill is needed.
FIG. 2 illustrates a water jet method among methods for detecting flaws in steel plates using noncontact ultrasonic detection methods.
The water jet method is a method of spraying water to a steel plate to provide a water path and transmitting and receiving ultrasonic waves through the water path. Since it is unnecessary to deposit an entire steel plate in a bath, the waterjet method described above has the advantages of more easily providing for facilities than the submersible ultrasonic detection method.
Referring to FIG. 2, water storage rolls 6 are installed in the front and rear of an ultrasonic probe 2 along a longitudinal direction of a steel plate 3, water is supplied through a nozzle 7 and a water supply pipe 8 to store a certain amount of water, and then ultrasonic detection is performed above the steel plate 3. In this case, even when a steel plate is moved, there is an advantage that the ultrasonic detection is still possible through rotation of the water storage rolls 6.
However, even in such a case, since it is impossible to store water when a front end and a rear end of the steel plate 3 enter the detection region, it is impossible to detect a corresponding portion. Also, when the width of a steel plate changes, there is a problem where stored water falls through both edge portions of the steel plate.